In many electric drive machines, an alternating current generator is used to provide electrical energy to drive the electric motor of the machine. Typically, the generator supplies a current to the motor, which is operatively coupled to the ground engaging elements of the machine, resulting in the machine moving along the ground.
The voltage and current for the field winding of an alternating current generator are often supplied from a voltage regulator connected to a voltage source. The voltage from the voltage regulator is supplied either directly to the generator's field winding or to the field winding of an exciter. In the latter case the output of the exciter is in turn supplied to the generator's field winding. When a voltage is supplied to a field winding, a current is generated inside the field winding after a small time lag. In most applications, the time lag may be insignificant and therefore, tolerable for the particular application. However, there are some applications where a prolonged time lag may hinder performance.
For instance, an operator wanting to move an electric drive machine up along an incline, needs nearly instant power from the motor to prevent the machine from rolling down the incline. Currently, upon pressing the accelerator of the electric drive machine, the operator either allows the machine to roll down the incline until the motor receives enough current to move the machine up the incline, or the operator engages the brakes of the machine to prevent it from rolling down until the motor receives enough current from the generator to move the machine up. However, engaging the brakes until the motor receives sufficient current may result in an undesirable jerky motion upon release of the brakes. Therefore, the operator must time the release of the brake accordingly to minimize the jerk, or allow the machine to roll down until the motor can move the machine forward.
In typical predecessor machines, the operator communicates an electrical signal to an electronic controller of the machine by pressing the accelerator. Although the electronic controller quickly sends the signal to the generator, the generator does not instantly produce a current in the output winding of the generator, which is in electrical communication with the motor. Rather, there is a response time before which the current begins to flow in the output winding of the generator.
Conventional wisdom in the industry teaches the use of a self-exciting apparatus to control the power output of the generator to the motor. U.S. Pat. No. 4,264,856 teaches the use of a capacitor to maintain a predetermined exciter output current. Furthermore, the capacitor is not electronically connected to an external power voltage source, but rather recharges itself via a feedback capability. This reference recognizes the need for providing a larger output current depending on the demand requirements of the motor but the industry thus far has failed to address the issue of shortening the time lag.
The present disclosure is directed toward at least one of the problems set forth above.